Grease a shallow small baking dish with nonstick spray and set aside
Melt 1 Tablespoon butter in a medium skillet until melted.
Add onion and saute until tender (about 5 minutes)
Add flour and mix well, cooking for about 1 minute.
Whisk in milk and cream and stir constantly to prevent lumping. Simmer for about 1 minute.
Stir in cheese and mix until smooth and melted (break into chunks to melt faster).
Remove from heat and add spinach, Parmesan, lemon zest and salt/pepper/nutmeg to taste.
Transfer to the baking dish.
Mix bread crumbs, remaining 1 Tablespoon butter (melted), olive oil and salt/pepper, to taste.
Top spinach mixture with bread crumb mixture (pat crumbs down to adhere them to the spinach mixture). Can cover and refrigerate at this point and bake later, if desired.
Bake for 20-25 minutes or until top is golden brown and sauce is bubbling.
Nutrition Info Per Serving: Calories 357 Total Fat 31 g Cholesterol 83 mg Sodium 311 mg Potassium 309 mg Total Carbohydrate 14 g Dietary Fiber 2 g Sugars 6 g Protein 8 g